What are CORBA Callbacks

Dominique Sacre · 2013-05-17T17:43:00+00:00

Summary This article describes how and when CORBA Callbacks should be used and the advantages and disadvantages they offer. Article Number 19429 Environment Orbix 6.3 All Supported Operating Systems Question/Problem Description What is a CORBA Callback?How to implement callback operations in Orbix.Implementing CORBA Callbacks.Advantages to CORBA Callbacks. Clarifying Information Error Message Defect/Enhancement Number Cause A typical CORBA exchange involves Application A (The client) invoking an operation on Application B (The server). The operation blocks until Application B returns a result, or an exception is thrown.In certain circumstances, it may be preferable for Application A to invoke an operation on Application B, but for this call not to block. Instead Application B could reestablish a connection to Application A and push back its reply. This approach is called a "CORBA Callback".In the above example, Application B takes on the role of a client, while Application A takes on that of a server. Resolution CORBA Callback objects are implemented on a client in exactly the same was as CORBA objects are on a server. CORBA Callback objects are activated in a client-side POA (Please see the section “Activating CORBA Objects” in our CORBA Programmers Guide). The CORBA Callback object's POA’s life-span policy should be set to TRANSIENT. Thus, all object references that the POA exports are valid only as long as the POA is running. This ensures that a late server callback is not misdirected to another client after the original client shuts down. As the root POA always exports transient object references, it may be appropriate to use a client’s root POA for callback objects. Using this approach, it is important to ensure the callback code is thread-safe, otherwise, the POA should be created with "SINGLE_THREAD_MODEL" and "TRANSIENT" policies. Workaround Notes For further details on implementing CORBA Callback objects, please see the section entitled "Implementing Callback Objects" in the Orbix Programmer's Guides. Attachment Created date: 06 September 2011 Last Modified: 13 February 2013 Last Published: 23 June 2012 First Published date: 10 September 2011 #KnowledgeDocs#Orbix

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May 17, 2013
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Dominique Sacre
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Summary	This article describes how and when CORBA Callbacks should be used and the advantages and disadvantages they offer.
Article Number	19429
Environment	Orbix 6.3 All Supported Operating Systems
Question/Problem Description	What is a CORBA Callback? How to implement callback operations in Orbix. Implementing CORBA Callbacks. Advantages to CORBA Callbacks.
Clarifying Information
Error Message
Defect/Enhancement Number
Cause	A typical CORBA exchange involves Application A (The client) invoking an operation on Application B (The server). The operation blocks until Application B returns a result, or an exception is thrown. In certain circumstances, it may be preferable for Application A to invoke an operation on Application B, but for this call not to block. Instead Application B could reestablish a connection to Application A and push back its reply. This approach is called a "CORBA Callback". In the above example, Application B takes on the role of a client, while Application A takes on that of a server.
Resolution	CORBA Callback objects are implemented on a client in exactly the same was as CORBA objects are on a server. CORBA Callback objects are activated in a client-side POA (Please see the section “Activating CORBA Objects” in our CORBA Programmers Guide). The CORBA Callback object's POA’s life-span policy should be set to TRANSIENT. Thus, all object references that the POA exports are valid only as long as the POA is running. This ensures that a late server callback is not misdirected to another client after the original client shuts down. As the root POA always exports transient object references, it may be appropriate to use a client’s root POA for callback objects. Using this approach, it is important to ensure the callback code is thread-safe, otherwise, the POA should be created with "SINGLE_THREAD_MODEL" and "TRANSIENT" policies.
Workaround
Notes	For further details on implementing CORBA Callback objects, please see the section entitled "Implementing Callback Objects" in the Orbix Programmer's Guides.
Attachment